Objects It is a principal object of the invention to provide a method of sandblasting embodying means to prevent the spread of the blast.

It is a further object oi the invention to provide a method in which the blasting abrasive can be recovered for further use.

It is a still further object to provide a simple and convenient apparatus for carryhig out this method.

In ordinary methods of sand blasting employ ing air as the propellant fluid, the abrasive material is after leaving the blasted surface, scat= tered about indiscriminately. As a consequence, the operator and others in the vicinity of the operations are subjected to the danger or inhaling abrasive particles. Frequently, sandblasting op erators develop silicosis, or at least must ire quently be removed from the job lest they do.

i To avoid these consequences, a method has been developed in which water is used to propel the sand. This has the disadvantages of both reducing the sheet of the abrasive by wetting it before impact with the blasted surface and or" requiring high water pressure to operate.

By the present method these disadvantages are avoided and positive advantages provided as well. According to this method, a jet of sand is propelled by air pressure from a centrally disposed nozzle and a blanketing screen of water projected outside the sand jet. The water does not come into contact with the sand before the latter reaches its objective but the screen created by the water catches the sand and other particles rebounding from the treated surface. In this way, the sand is prevented from spreading and at the same time it is carried away in the water stream so that it may be collected for re-use.

A preferred apparatus for carrying out this process is featured by a central tube through which the sand is projected and a concentrically arranged nozzle structure connected to this tube. This nozzle is adapted to project a frustro-conical stream or sheet of water. Means are provided in the nozzle for adjusting the velocity of the sheet while the tube through which the sand is carried may be made renewable to allow easy replacement.

Drawing Having thus generally described the invention, reference will now be made to the accompanying drawing which illustrates a preferred form of apparatus according to the invention, and in which:

Figure 1 is a fragmentary cross section through this preferred form of apparatus.

Figure 2 is a horizontal cross section as along the line 22 of Figure l.

-Figure 3 is a frontal elevation of the device of Figuresl and 2.

Figure s is a reduced elevational view illustrating a portion oi thedevice of the previous figures and the method of the present invention.

Referring more particularly to the drawing, the sand blast apparatus is made up of a body A, for instance, a casting or otherwise formed part. This body is formed with a longitudinal central opening it receiving a removable tube i i forming a passage for the sand or other blasting material. A set screw it) extending through a boss 53 on the body secures the tube ii in place.

Mounted on the body A is a jacket is having 7 at one end outwardly flared portions 66 forming control therefor.

a mouth. At the other end, the jacket it includes an annular flange ii engaging the body A. The body includes upstanding bosses 26 to which the jacket is screwed by means of set screws 2 l. The jacket it also includes a threaded connection 25 constituting an inlet to which the threaded end of a water pipe 26 is connected.

The forward end of the body is threaded as at he to receive a threaded frustro-conical ring or plug iii. The ring 36' is adapted to cooperate with the flared portions it of the Jacket 55 to form a nozzle and may be screwed inwards or outwards to vary the clearance between its tapered face and the inner surfaces of the flared portions l8 whose taper approximates that of the ring. A lock-nut 9% is provided to lock the ring in the desired position.

Operation In operation, the tube ii is connected With a suitable source of sand and air pressure and a The jacket 15 is connected through the pipe 26 with a suitable source of water pressure and a control for the pressure. Thus connected, the device is ready for use in sand blasting for the purpose of cleaning or conditioning surfaces to receive paint, etc. When both air and water pressures are turned on, the air-sand jet C is projected substantially as noted in Figure 1 against the surface B to be treated.

The water is projected in a conical sheet D about the sand blast.

V The sand is projected by the blast. and flying away from the surface is caught by the water sheet which carries it away in a stream from which it may be recovered for further use.

The amount of pressure in the air line varies relative to the surface being treated. For instance, in the case of blasting sandstone or alumimm: 20 to 50 lbs. per square inch pressure is satisfactory. For steel or hard stone the pressure required will be in the order of 80 lbs. per square inch. It is not necessary to have heavy water pressure as the only function of the water is to form a screen to catch the blast particles. A relatively low water pressure of 25 to 50 lbs. has been found satisfactory. It should be understood that these figures are merely illustrative and are not to be taken in a limiting sense.

This method has great advantages. The sand does not come into contact with water until after it has impinged on the surface being treated. The sand can easily be recovered from the water stream which carries it away.

High pressure water is not necessary. The only function of the water is to form a protective sheet to concentrate the blasting abrasive.

It will be understood that the word sand has been used for convenience to express the abrasive material and that this term can be expanded by the doctrine of equivalents to cover other abrasives which might be used for the same purpose. Similar remarks apply to th terms air and water.

Any suitable material can be chosen for the manufacture of the parts of the blasting apparatus. For instance, cast iron pipe has been found satisfactory for the sand-air line H as this material can be renewed frequently at a low cost. l

Whil no pressure equipment or controls are shown in the drawing, it is understood that the method presumes the use of suitable plant together with controls for regulating the flow of sand, air and water.

It will be understood that various modifications may be made in this invention without departing from the spirit thereof or the scope of the claims, and therefore the exact forms shown are to be taken as illustrative only and not in a limiting sense, it being desired that only such limitations shall be placed thereon as may be imposed by the state of the prior art or are set forth in the accompanying claims.

I claim:

1. A sandblast apparatus, comprising, a bodyhaving an inlet end and an outlet end and a passage extending therebetween,v a liner adapted for carrying sand and air removably mounted in said passage, a water jacket surrounding at least a portion of said body and having a flared portion adjacent said outlet forming a conical -mouth, a frustro-conical plug connected to said 10 body for axial movement in relation thereto, said plug being adapted to form with the flared mouth of said jacket a frustro-conical water discharge nozzle of adjustable width, 0. water communication to said jacket, and a communication to said liner for sand and air.

2. A sandblast apparatus as claimed in claim 1 wherein said body includes a threaded portion adjacent the discharge end and said plug is provided with a corresponding threaded portion mating with the threaded portion of said body.

3. The method of sandblasting comprising projecting a stream of substantially dry abrasive 4. The method of sandblasting comprising projecting a stream of substantially dry abrasive particles against a surface being treated, simultaneously projecting a co-extensive continuous substantially frustro-conical enclosing sheet of water, whereby a substantially transparent protective shield is formed about the particle stream to entrain particles emanating from the surface being treated.

5. The method of sandblasting comprising projecting a stream of substantially dry abrasive particle against a portion of a surface being treated, simultaneously projecting a co-extensive continuous enclosing sheet of water against said surface in surrounding spaced relation to said portion being treated, whereby a substantially transparent protective shield is formed about the particle stream from the source of projection of the abrasive particles to the surface being treated.